1. Field of the Invention
The present invention relates to an ABS (Air-Bearing Surface) shape correction method for a slider provided on the tip portion of a magnetic head, and an ABS shape correction apparatus for a slider of a magnetic head.
2. Description of Related Art
FIG. 1 is a perspective view schematically showing one example of a slider of a magnetic head that has an ABS. In FIG. 1, a reference number 1 denotes a slider of a magnetic head that faces a magnetic disk. In order to keep a constant floating volume above the slider, floating surface rails 2, 3 and 4 are provided. During a recording or a reproduction of a magnetic disk, the floating surface rails 2 to 4 face the surface of the magnetic disk (not shown).
Based on the existence of the floating surface rails 2, 3 and 4, a constant distance is maintained between the magnetic disk and the surface of the slider. In other words, a constant floating height of the slider is maintained. This constant floating height is maintained for the following reason. When there arises a difference between the pressure in the gap formed between the magnetic disk and the portions where the floating surface rails exist and the pressure formed between the magnetic disk and the portions where the floating surface rails do not exist, the pressure is balanced between these two gaps.
The surface of the floating surface rails will be called an ABS. The surface of the slider at portions where there is no floating surface rail, that is, the surface of the slider facing the surface of the magnetic disk, will also be called an ABS. In order to prevent the ABS from being adsorbed by the magnetic disk and, also, in order to stabilize the floating characteristics of the slider, the ABS must be a flat surface, in general, except in the case where the ABS has a special shape. Particularly, flattening of the ABS has been increasingly required under the current situation where the floating height between the magnetic disk and the ABS becomes smaller with a reduction in the size of the magnetic head.
However, the ABS is distorted for various reasons. The distortion of the ABS is classified into the following three types. As schematically shown in FIG. 1, the ABS is distorted in a direction parallel to the rotation direction of the magnetic disk. This is called a crown. The ABS is also distorted in a direction orthogonal to the rotation direction of the magnetic disk. This is called a camber. A third type of distortion is that the ABS is distorted in a direction twisted from the rotation direction of the magnetic disk. This is called a twist.
To flatten the ABS, radiation of energy such as a laser beam, a diamond point or an ion mill is applied onto the ABS or its rear surface, thereby correcting the shape of the ABS. In other words, when one of these types of radiation is applied onto the ABS, the stress of the ABS changes. Thus, the distortion of the ABS is corrected. In this case, the correction volume is different depending on a processing condition such as the size of the irradiation energy.
The processing conditions of the ABS may be determined based on a visual observation of numerical values of crown or camber obtained from an exclusive apparatus for measuring the shape of the ABS or values given on a display according to a light interference method or the like.
As a conventional ABS shape correction method, the method as disclosed in Japanese Patent Application Laid-open Publication No. Hei 6-84312 has been known.
FIG. 2 is a side view of a conventional slider having a crown-shaped ABS and a magnetic disk as disclosed in Japanese Patent Application Laid-open Publication No. Hei 6-84312. In FIG. 2, a reference number 21 denotes a slider of a magnetic head, 22 denotes an arm of the magnetic head, and 23 denotes a magnetic disk. As shown in FIG. 2, the slider 21 has a crown shape distorted in a direction parallel with the rotation direction of the magnetic disk 23. The line of a mountain ridge of this crown shape is in line contact with the magnetic disk 23.
In the conventional slider shown in FIG. 2, it is desired that the ABS is in a crown shape, and it has been a main object to correct this crown shape. For this purpose, a method has been employed that a centerline position of the slider in a longitudinal direction is line scanned by an He-Ne laser beam or the like, and the crown volume is measured from an expanded angle of a reflection beam, and processing conditions are determined based on a result of this measurement. In order to control the crown volume, a plurality of straight lines are processed or a wide area is processed, based on the centerline position of the slider in principle.
According to the above publication, however, there is no clear expression about what type of pattern is to be processed. The publication only discloses that, for correcting a distortion in the crown direction, a plurality of straight lines are processed in a direction forming a right angle with the crown, and for correcting a distortion in the camber direction, a plurality of straight lines are suitably processed in a direction forming a right angle with the camber.
Further, there is no clear disclosure about a control method for correcting to a particularly desired shape.
FIG. 3 is a side view of a stiction free slider provided with legs on the surface that faces a magnetic disk in order to prevent an adsorption, and a magnetic disk. In FIG. 3, a reference number 31 denotes a slider, 32 denotes an arm, 33 and 34 denote legs for preventing adsorption, 35 and 36 denote floating surface rails, 37 denotes a read/write element provided on the slider 31, and 38 denotes a magnetic disk. In this case, the surface of the floating surface rails 35 and 36 is an ABS.
In this slider provided with the legs for preventing adsorption, it is required that the ABS is formed in a flat shape instead of a crown shape as disclosed in the above publication.
The present invention is intended to provide an ABS having a flat shape.
The ABS of a slider as shown in FIG. 3 receives a mechanical deformation due to grinding during a process of processing the slider, or by a residual stress due to lapping. Based on the combination of the shapes of the floating surface rails 35 and 36 formed by the dry etching processing and ion mill processing, the ABS does not have a simple shape of any one of the defined crown, camber and twist, but tends to have a more complex shape. Therefore, in order to correct the ABS shape with higher precision, it is necessary to evaluate the shape of the whole surface. However, according to the method disclosed in the above publication, only the position of the centerline of the slider is recognized, and the evaluation of the whole shape of the ABS has been insufficient.
Further, according to the method of determining processing conditions by visual observation of a result of the measurement, it is only possible to determine a bottom position or a position of a line of a ridge based on intuition. Thus, it has been difficult to automatically and accurately determine a processing position.
Further, when various factors such as processing conditions and material characteristics are always constant, it is always possible to carry out a stable correction by setting constant processing conditions, and a satisfactory correction can be obtained by one process. However, in actual practice, it has been difficult to always carry out a stable correction because of factors such as the surface state of the slider, the components of the materials, and the processing machine.
The present invention has been made in the light of the above-described problems of the prior-art techniques. It is, therefore, an object of the present invention to provide an ABS shape correction method for a slider of a magnetic head and an ABS shape correction apparatus for a slider of a magnetic head capable of carrying out stable correction of the ABS with high precision in spite of changes in the surface state of the slider, the components of the materials and the characteristics of a processing machine, based on the idea of evaluating the shape of the whole ABS by measuring three-dimensional positions on the ABS of the slider of a magnetic head.
In order to achieve the above object, according to one aspect of the present invention, there are provided an ABS shape correction method for a slider of a magnetic head and an apparatus for implementing this method, the method comprising the steps of measuring three-dimensional positions on the ABS, interpolating the measured points based on data obtained by this measurement, thereby generating an interpolated surface, then calculating a processing center position of the magnetic head based on this interpolated surface, and finally processing a plurality of lines parallel with the processing center position.
According to this aspect, as the three-dimensional positions on the ABS are measured, it becomes possible to evaluate the shape of the ABS.
Further, according to the above aspect, as the three-dimensional measurement is not based on a visual observation, it is possible to automatically and accurately determine a processing position.
Further, according to the above method, it is always possible to carry out a stable flattening correction of the ABS with high precision, without regard for the surface state of the slider, the components of materials and the characteristics of a processing machine.